Gas Separation & Purification最新文献

Adsorption of pure methane, ethane and ethylene on molecular sieve zeolites was examined via the gas chromatographic method to determine the potential for the separation of ethylene from light hydrocarbons. The molecular sieves chosen for the study were H-mordenite and 13X, CaX, 4A and 5A zeolites. Henry's law constants were determined over a variety of temperature ranges between 233 and 473 K. van't Hoff plots are presented for all three gases on 4A and 5A zeolites and for methane and ethylene on the CaX and 13X zeolites and H-mordenite. Equilibrium separation factors for the ethylene/methane system are provided for all zeolites (except clinoptilolite) over various temperature ranges. Separation is most promising with CaX zeolite, which yielded separation factors ranging from 1100 at 100 °C to 100 at 200 °C. Separation seems possible in 5A and CaX zeolites at very high temperatures due to the strong affinity of their divalent cations for the ethylene π-bond.

Equilibrium concentrations of species and gas loading in aqueous solutions of alkanolamine loaded with CO₂ are being compared with predicted profiles obtained from the Deshmukh-Mather Model. A new technique is being proposed based on titration using a base, NaOH, to determine the concentrations of the different species at equilibrium. The technique is reliable and easy to perform to give reproducible results. Experimental and predicted concentrations of species are in good agreement over a range of gas loading between 0.4 and 1.0 for aqueous AMP solutions. For DEA, the predicted and measured values complement each other at high loading typically above 0.6. At low loading, there is a significant difference between the sets of values for carbamate and bicarbonate. These differences are likely due to the value of the equilibrium constant for the carbamate formation, which is taken as an adjustable parameter in the model, to give the best fit to the experimental data of either CO₂ partial pressure or gas loading.

Multicomponent adsorption equilibrium data are essential for the reliable design of processes and equipment for gas separation by adsorption. We discuss techniques for the measurement and analysis of multicomponent adsorption equilibrium data, and present a comprehensive set of equilibrium data for the adsorption of oxygen and nitrogen on 5A-zeolite.

In the present work the water gas shift reaction is considered as a particular application of a catalytic membrane reactor. Three different methods to deposit a thin film of palladium on a porous ceramic tubular membrane have been studied: the magnetron sputtering technique, the physical vapour deposition technique, and the co-condensation technique or solvated metal atom deposition method. For each composite membrane, characterization in terms of pore distribution, thickness of the film, percentage of Pd deposited along the thickness of the membrane and CO conversion versus feed flow rate and versus different $\text{H}{}_2\text{O}\text{CO}$ molar ratio are presented.

This paper models the performance of a membrane reactor. The membrane, a composite alumina-based one, is packed with a catalyst and allows low molecular weight gases to diffuse through it at a faster rate than gases with a higher molecular weight. This allows a greater conversion to be achieved in one pass through the reactor. The reaction that is specifically considered in this paper is the dehydrogenation of methyl-cyclohexane to toluene with the production of hydrogen. This latter species is preferentially removed by the membrane. Data for the performance of the membrane have been estimated from previous experiments using single gases and the mechanisms considered are Knudsen and bulk flow. Surface flow is not considered in the model as it is possibly not important as the endothermic reaction is carried out at a high temperature. A standard kinetic model is also incorporated in the calculations. The correlations of maximum effective length of membrane reactors and maximum percentage conversion as functions of the feed velocity and the membrane diameter are demonstrated in this paper. This paper also considers the behaviour of a compound reactor in which the first section is a straightforward ‘plug flow’ reactor where the catalyst is confined in an impermeable tube with the same internal diameter as the membrane. This is followed by a section containing the membrane. The reason for considering this configuration is to avoid unnecessary leakage of methyl-cyclohexane feed in the initial stages of the reaction. This innovation leads to predicted increases in the overall conversion of the process.

A scheme is presented for the calculation of the UNIFAC activity coefficient and its analytical derivatives with respect to mole fractions and with respect to temperature. A numerical example is also given.

The performance of a pilot test for biogas upgrading has been tested under different process conditions to produce oxygen-enriched air for aqueous media application. The selectivity of the polysulfone hollow fibres for $\text{N}{}_2\text{O}{}_2$ permeation allows the production of an oxygen-enriched air stream in the 30–50% range and an inert gas (nitrogen between 82–98%) by operating the pilot unit at different stage-cut values in a single pass mode. Membrane area requirements for a medium size plant of 100 Nm³ h⁻¹ are discussed according to a simple perfect mixing model for gas permeation.

A mathematical model has been developed to predict the rates of gas absorption in turbulent falling liquid films with and without the first order homogeneous reaction and external gas phase mass transfer resistance. The eddy viscosity model used to describe the flow distribution is the van Driest model, modified in the outer region of the film by the use of an eddy diffusivity deduced from gas absorption measurements. The results are given for special cases to illustrate the effects of turbulence, reaction rate and gas phase resistances on the concentration profiles and the rates of gas absorption.

Experimental data demonstrate that mixing of absorbents gives the possibility to increase gas solubility. This effect may be predicted using a simplified theory of solution. Solution theory predicts that increasing solubility is possible in mixtures with positive deviations from Raul's law and when some other conditions exist. This effect is greatest near lamination of solvent mixture. Gas solubility in regular solution may increase not more than 1.6 times. A similar effect may arise when mixing chemisorbents. This effect is very large. When an equal saturation degree of solution by gas is fixed, the equilibrium pressure of gas above solution may decrease by 10–50 times as compared with the pressure above the solution of one of the chemisorbents. Theory and experiment demonstrate that the positive effect is greatest when the saturation degree is small, and this effect becomes negative when the saturation degree is great. These results give a new explanation for the effect of chemisorbent mixing in industrial processes such as the Benfield process.

This paper presents linear driving force approximations for the dusty gas model in a bisolute system obeying linear or Langmuir isotherms, in two situations: when there is a nonnegligible surface flux in parallel with the diffusive and convective fluxes; and when there is a micropore resistance to mass transfer in series. The approximations were developed using a semi-empirical procedure that starts with the particle response to a square wave perturbation considering a simple diffusion/convection mechanism, and proceeds by consecutive corrections to this basic result. These corrections are obtained using superposition, similarity and pattern recognition. The approximations are good (average quadratic error ⩽10%) when representing the system cyclic steady state, whether the perturbations are sharp or smooth.